Discharge lamp lighting circuit

Abstract

A discharge lamp lighting circuit is capable of preventing the discharge lamp from going out unexpectedly. The discharge lamp lighting circuit includes a DC-AC inverter which receives a power source voltage, boosts and converts the power source voltage into AC and supplies AC electric power to the discharge lamp 21 . A control circuit sends a long cycle signal when the discharge lamp 21 is started. The cycle of the long cycle signal is longer than a frequency at the time of steady lighting. The control circuit sends a steady drive signal, which is a frequency at the time of steady lighting, to the DC-AC inverter 25 . A cycle of the long cycle signal is set according to at least one of the power source voltage, the temperature of the discharge lamp lighting circuit or the extinguishing time.

1. A discharge lamp lighting circuit for lighting a discharge lamp comprising:
 a boosting AC converter arranged to receive a power source voltage, boost and convert the power source voltage into AC, and supply AC electric power to the discharge lamp; and 
 a control circuit arranged to provide a long cycle signal to the boosting AC circuit converter to set a cycle for a DC period when the discharge lamp is started, the cycle of the long cycle signal being longer than a frequency at a time of steady lighting, the control circuit further being arranged to send a steady drive signal, which is a frequency at the time of steady lighting, to the boosting AC converter, wherein the control circuit is arranged to set the cycle of the long cycle signal according to the power source voltage and an extinguishing time. 
 
     
     
       2. The discharge lamp lighting circuit according to  claim 1 , wherein the control circuit is arranged to set the cycle of the long cycle signal to be longer as the power source voltage is decreased. 
     
     
       3. The discharge lamp lighting circuit according to  claim 1 , wherein the control circuit is arranged to set the cycle of the long cycle signal to be longer as the extinguishing time is increased. 
     
     
       4. The discharge lamp lighting circuit according to  claim 1 , wherein the control circuit is arranged to set the cycle of the long cycle signal according to a temperature of the discharge lamp lighting circuit, and the control circuit is arranged to set the cycle of the long cycle signal to be longer as the temperature of the discharge lamp lighting circuit is raised. 
     
     
       5. The discharge lamp lighting circuit according to  claim 1 , wherein the control circuit is arranged to set the cycle of the long cycle signal at dispersed values.